Dil, in U.S. Pat. No. 4,209,804, teaches a reflective information recording structure which contains prepressed V-shaped grooves in which data may be recorded by local melting of the reflective metal coating by a laser. The data on the media is read by means of optical phase shift effects. Since the preformed grooves are at an optical phase depth of 95 to 140, the reading laser must be of the precise wavelength corresponding to the groove depth. The information area has a width of approximately 0.6 microns, so a thick protective substrate, usually 1200 microns deep is used to ensure that one micron surface dust particles are out-of-focus for the read beam.
Such thick protective materials cannot be used for wallet cards which have a total thickness of only 800 microns under ISO (International Standards Organization) standards and further it would be uncomfortable to carry a rigid card in trouser pockets or wallets. Also, it is difficult to bond a phase sensitive recording/reading surface to a protective laminating material with an adhesive without introducing a varying phase shicft across the surface. It is also impractical to melt large holes since a large lip would be formed around the hole causing a great distortion of the phase shift. Edge transition of the hole is the phase shift which is measured, and since the height of the lip is directly proportional to the square root of the hole diameter, phase shift reading is only practical for small holes. For example, a 25 micron diameter hole creates a lip with one micron height, which is much larger than the wavelength of the reading beam. Thus for large holes and bonded protective materials it is desirable to have a recording/reading structure that does not rely on phase shifts.
Lahr in U.S. Pat. No. 3,873,813 teaches a debit card in which use is indicated by alteration of a spot of heat sensitive coating in a selected area thereby permanently changing the reflective characteristics of that area. A reflective heat sensitive material becomes transparent on heating, thereby exposing an underlying strip of black paper which then absorbs the light energy. Recording requires exposure to a high intensity light beam for 0.7 second to raise the temperature of the material to 175 F. and an additional 5 milliseconds above 175 F. This type of credit card system permits recording of less than two data bits per second. Because of the retained, diffused liquid, the sizes of the data spots are large and difficult to regulate. This card requires a blue read beam, therefore scratches and surface dust will cause a large number of data errors unless very large data spots are used that reduce capacity to under 10,000 bits. While this data capacity is satisfactory for some debit and credit cards, it is unsuitable for detailed recording of text of books, journals, manuals, catalogues, directories and other published works. Also, the recording rate of less than two bits per second would make it unacceptable for use in most applications. Another disadvantage of this card is that all of the data is destroyed if its temperature reaches 175 C., for example on the dashboard of a car or if passed through a household washer and dryer.
Nagata in U.S. Pat. No. 4,197,986, Girard in U.S. Pat. No. 4,224,666 and Atalla in U.S. Pat. No. 4,304,990 teach updating of data cards. Nagata teaches the updating of maximum limits and balance on a card in which the complete data file is in an auxiliary memory circuit such as a magnetic disc or drum. A sales slip containing the transaction is recorded separately from the card. Giraud teaches a data-processing machine-access card containing an integrated circuit chip with a memory bank. The memory stores predetermined items of confidential data intended to authorize or prevent access to the machine. Only the balance is updated.
Atalla teaches a card in which only the balance is recorded and updated. This card can only be used where the transaction system is connected to a central computer. None of these cards has the memory storage capacity needed to accumulate records of past transactions, nor to add annotations and other information related to these records.
Various recording media have been developed for use on a rotating disc format. Because the disc is spinning rapidly, short laser pulse times (on the order of 500 nanoseconds) are necessary to confine the heating to small spots. The media have been developed to increase the sensitivity to the beam by varying the parameter of media absorptivity. Spong in U.S. Pat. Nos. 4,190,843 and 4,305,081 puts an absorptive dye layer over a reflective aluminum layer. Spots are recorded by ablation of the dye layer exposing the underlying reflective layer. Bell in U.S. Pat. No. 4,300,143, teaches a similar technique. Bartolini in U.S. Pat. No. 4,313,188 adds a protective layer between the dye layer and the reflective layer. Wilkinson in U.S. Pat. No. 4,345,261 uses a light absorptive silica dielectric layer in place of the dye layer. Terao teaches an inorganic absorptive layer over an organic recording film layer. Holes are formed in the film layer by heat generated in the absorptive layer. Suzuki in U.S. Pat. No. 4,202,491 uses a fluorescent ink layer on which data spots emit infrared radiation. Improved sensitivity is obtained in these media at the expense of extra layers which increase complexity and cost. This increased sensitivity is not necessary for a card format.